[llvm][NFC] Cache FAM in InlineAdvisor

Summary:
This simplifies the interface by storing the function analysis manager
with the InlineAdvisor, and, thus, not requiring it be passed each time
we inquire for an advice.

Reviewers: davidxl, asbirlea

Subscribers: eraman, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80405